A technique has conventionally been known that an electric current is detected using one shunt resistance inserted into a direct-current part of an inverter circuit when U-, V- and W-phase currents are detected for the purpose of controlling an electric motor. In order that all the three-phase currents may be detected in the above-mentioned manner, a three-phase PWM (pulse width modulation) signal pattern needs to be generated in one period of a PWM carrier so that two or more phase currents are detectable. For this purpose, a motor control device has been conventionally proposed which can normally detect two or more phase currents by shifting a phase of the PWM signal in one period of the PWM carrier, without increase in noise. See Japanese Patent No. 5178799, the contents of which are incorporated herein by reference.
However, the above-described conventional current detection manner results in a problem that only one phase current can be detected in two occurrences of current detection timing in a region where a modulation factor is increased.